This invention relates to a printer for printing image information onto a recording medium and, more particularly, to a system for regulating a widthwise printing start-up position on the recording medium in accordance with a width thereof.
Conventinally, there is known an image recording apparatus utilizing a so-called electrophotographic system in which a charged surface of a photoconductive drum is exposed to light to form a latent image on the charged drum surface. Toner is then applied to the latent image to develop the image, and the developed image is transferred onto a recording medium and fixed by a fixing unit. Such an image recording apparatus is chiefly employed in a copying machine. In recent years, however, the image recording apparatus is also being utilized printer and the like for printing out information outputted from a computer. Further, in the copying machine, cut sheets are generally used as the recording medium. In a printer, however, it is desired to use, as the recording medium, a continuous recording form that is identical with that used conventionally in a line-printer or the like.
The continuous recording form is a folded continuous recording form (hereinafter referred to simply as "continuous form") called a fan-folded form, which is folded into a predetermined length and which has sprocket holes formed in opposite side edge portions of the fan-folded form. Perforations are provided at each of the folded sections to enable the sheet sections be easily severed from each other. In this connection, there are several types of continuous forms different in width from each other, such as, for example, continuous forms of 10 inches in width, 15 inches in width and so on. One of these continuous forms is suitably selected, depending upon the image information to be recorded.
In the above-described image recording apparatus utilizing the electrophotographic system, a guide mechanism is arranged along a transport path of the continuous form or the like serving as a recording medium, for guiding the continuous form along the transport path. When a recording medium is the continuous form, the guide mechanism generally comprises a pair of endless tractor belts which are arranged parallel to each other along the transport path. Each of the tractor belts is formed with a plurality of projections which are arranged along the tractor belt and which are engageable with sprocket holes provides along a corresponding one of the opposite side edge portions of the continuous form. The continuous form is guided so as to travel along the predetermined transport path, with the projections on the respective tractor belts fitted in the sprocket holes in the respective side edge portions of the continuous form. When the continuous form is replaced by another one having a different width, both tractor belts are moved either towards or away from each other in accordance with the width of the new continuous form, such that the projections on the tractor belts are engaged with the sprocket holes in the respective side edge portions of the new continuous form.
Generally, however, since both tractor belts of the guide mechanism are moved toward and away from each other widthwise of the continuous form by respective distances equal to each other, the position of the continuous form along the transport path, that is, both the widthwise side edge positions of the continuous form associated with the printing start-up and termination positions vary because of replacement of the continuous form by another one having a different width. Accordingly, unless the moving amount of each of the tractor belts is known, the widthwise printing start-up timing shifts with respect to the new continuous form which has the different width, so that printing cannot regularly or correctly be effected widthwise for the continous form.